The head-up display devices, whether worn or not, make it possible to display in particular a “symbology” conforming to the outside world, that is to say a set of symbols whose position in front of the eye or the pilot allows for a superimposition with the corresponding elements in the outside real world. It can be for example a speed vector, a target on the ground such as a symbol representing a landing runway, a synthetic representation of the terrain or even a sensor image.
This conformal display requires knowledge of the position and of the attitude of the aircraft and, for head-worn display devices, the attitude of the display relative to a fixed reference linked to the aircraft. These different positions and attitudes are supplied by the avionics systems for those of the aircraft, and by the posture detection device DDP for those of the display.
For example and in particular, the avionics systems for supplying the position and the attitude of an aircraft can be:
a global positioning device of GPS (Global Positioning System) type; and
an inertial reference system IRS based on gyroscopes and accelerometers of MEMS (Microelectromechanical Systems) type or on a laser gyroscope, or an attitude and heading reference system AHRS.
As is known, a harmonization of the head-up display system is performed on installation of a head-up display system, worn or not worn, in the cockpit in order to compute the correction of angles to be made to switch from the display reference frame to the aircraft reference frame, and in order to obtain a conformal head-up display.
To date and as is known, the avionics system for supplying the attitude of the aircraft relative to the Earth, hereinafter called attitude inertial device, is:
rigidly secured to the platform of the aircraft, which requires a lengthy harmonization procedure to align said attitude inertial device on said platform, or
attached to the fiducial device linked to the platform, which also requires a lengthy harmonization procedure to align said fiducial device on the platform of the aircraft.
Many platforms of aircraft such as, for example, helicopters or light aeroplanes are not these days equipped with conventional inertial means for supplying their own attitude relative to the Earth but recently it has become possible to use small inertial equipment items capable of suppling the pilot with this attitude information with relatively correct performance levels. These equipment items can easily be packaged in removable modules that can be “attached by suction”, that is to say fixed using a sucker, onto the windshield of the supporting structure of the cockpit. Such inertial equipment items of small size also include a device for supplying the position of the equipment item and therefore of the aircraft.
According to a first drawback, the removable nature of this inertial equipment item with a new fixing configuration each time said inertial equipment item is moved requires the implementation of a procedure for a new humanization of the conformal display system that is accurate and rapid.
According to a second drawback, this inertial equipment item knows the heading of the aircraft with relatively little accuracy in the absence of movement of the platform. Indeed, the presence of a positioning device, of GPS type, incorporated in the equipment of item, and of hybridation algorithms, make it possible to refine the knowledge of the heading during the changes in the movement of the aircraft, but on the ground, before take-off, the value known for the heading is relatively incorrect.
A first technical problem is how to provide a worn head-up display system for making the display of piloting information of an aircraft conform with the outside real world and the method for mutual harmonization of the elements of said head-up display system which make it possible to rapidly and accurately know the relative orientation of the attitude inertial device of the removable inertial equipment item, that can easily be moved, relative to the fixed fiducial element linked to the platform, also constituting the fixed element of the posture detection subsystem DDP.
A second technical problem is how to provide a worn head-up display system and a harmonization method which make it possible to rapidly and accurately know the relative orientation of the attitude inertial device of the removable inertial equipment item, that can easily be moved, relative to the fixed fiducial element linked to the platform, and the relative orientation of the display of the worn head-up display system relative to the mobile tracking element of the posture detection subsystem DDP.
A third technical problem is how to provide a head-up display system for making the display of piloting information of an aircraft conform with the outside real world and a harmonization method which makes it possible to rapidly and accurately know the relative orientation of the attitude inertial device of the removable inertial equipment item, that can easily be moved, relative to the platform of the aircraft.